Question

I know that a function pointer stores the address of a function.

int fun(int x){
 //return something
} 
int (pfun*)(int)=&fun;

int main(){

std::cout << &fun << "\n"; // this print out 1
std::cout << fun << "\n" ; // this print out 1
std::cout << &pfun << "\n"; // this print out 0x0022ff40
std::cout << pfun << "\n" ; // this print out 1

 }

So my questions are :
1) if the fun() doesn’t even have an address how can pfun does point to fun().
2) for example in dynamic binding when I use a pointer function at runtime. does the compiler change pfun value to a real pointer like 0X….. so that at runtime will know which function to call since the names doesn’t existe after compilation?

Answer 1

The expressions fun and &fun have the same meaning: &fun which is equivalent to the value stored in pfun, so it is no wonder that the three of them yield the same output. &pfun is the address of the pointer, which is the address of the variable.

Now the question is why 1… well, the answer is that there is no overloaded operator<< that takes an std::ostream and a function pointer, so the compiler tries to find the best match among the existing overloads which happens to be bool (a function pointer is implicitly convertible to bool). The function pointer will be converted to false only if the function pointer is null, which is not the case. The true value is finally printed as 1 (you can check this by doing: std::cout << std::boolalpha << fun which will print true).

If you want to obtain the actual address of the function (in this process) you can force the cast to a void pointer and print the result. This might not be technically correct, but it will give you a number different than 1… Note that the value might differ in different runs and basically has no meaning at all.